The purpose of the proposed research work is to examine excitation contraction coupling in vascular smooth muscle and in particular coronary arterial smooth muscle to various mechanistically different vasoconstrictor and vasodilator agents with relation to Ca ions and Mg ions movements and to evaluate the role these ions play in regulating the tone of these blood vessels. The control of intracellular concentration of the ions will be studied by changing the concentration of Ca ions and Mg ions in the medium, by evaluating the influence of divalent ion carrying ionophore, A 23187. The subsequent changes in vascular smooth muscle Ca ions and Mg ions movements will be studied by measuring cellular ion fluxes, membrane potentials and total Ca ions and Mg ions content of the muscle by atomic absorption spectrophotometry. The changes in c-AMP and c-GMP and ATP will also be measured in correlation with the altered contractility of vascular smooth muscle with relation to changes in Ca ions and Mg ions concentrations in the medium. These studies will be conducted on a comparative basis utilizing another vascular smooth muscle from different vascular bed and of different species. The information obtained from these studies will be useful in understanding the pharmacology and physiology of vascular smooth muscle with relation to excitation contraction coupling during both normal and altered physiological conditions. In addition, the data obtained in these studies may have relevance to control in other cellular systems involved in excitation contraction coupling or excitation secretion and coupling.